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The Liers plain was dug by one of the glacial tongues of the Rhône then filled in by fluvial-glacial alluvial deposits. The relief is very discreet in the valley bottom, but the general slope is not negligible, with a 150m/492ft drop between the eastern and western extremities.

The drainage system now consists of only a few temporary run-offs in the downstream part.

The land is used for agriculture (cereals, sown pastureland and maize), with only moderate urbanization. It is crossed by three large roads (A 48, N 85, D 518) and is far from any major urban centres.

The plain's features resemble those of the Bièvre Plain, from which it is separated only by Banchet Hill. The resemblance is so great that it seems the two form a single space of large-scale crops, on which the thin spine of the hill has been placed.

On the eastern part, east of D 518, there are the same types of spaces as in the Bièvre Plain, completely empty of housing and crossed only by a few transversal roads. In the western part, west of D 518, the landscape structure is similar to that of the Côte-Saint-André Plain, with a more extensive system of transversal and longitudinal roads linking several homes situated on the wooded edge of the terrace left by the retreat of the Quaternary glaciers.

The contrast between the plain and the hills is so great that the villages located at the foot of the northern and southern hills seem to belong more to the hills than to the plain itself. This contrast also points to the need for a plan to develop local country lanes, along with tree plantations, which would help re-establish certain ecological and landscape continuities.